Re: 6MAN Adoption call on raft-chakrabarti-nordmark-6man-efficient-nd-04

[Lorenzo Colitti <[e-mail]>]

On Thu, Nov 21, 2013 at 3:40 AM, Pascal Thubert (pthubert) <
[e-mail]> wrote:

> So clearly, as we build a multilink subnet with 802.15.4 at the edge, we
> must place a router - called backbone router in ISA100.11a - between the .1
> and the .15.4 links. You will note that even in that case, we need the
> registration mechanism to perform DAD - RFC 6775 was initially designed in
> that context -, and that proxy ND can be used at the backbone router, as
> discussed in the original ML subnet draft by Dave and Christian.
>

If you're routing, why do you need proxy ND? Just give the 802.15.4 network
a separate /64 and run 6LoWPAN ND inside it.

I think that's when Erik says "merging two link types is not the solution",
that's what he means. I think he's just suggesting that you use existing
standard ND in the high-powered network and existing 6LowPAN ND in the
low-power network, and just route between them. That way you don't have to
define a new ND protocol.


> Now, WiFi does not qualify as 'a different link type' that would require
> routing to Ethernet; on a same AP, some clients may be low power


Well, but isn't wifi fundamentally unsuited for low-power networks anyway?
It's got beacons going all the time, it has multicast, etc.


> We do not want to renumber each time a device re-associates to the next
> AP, so we care for a rather large subnet. And there, it is not just a
> problem of implementing multicast at layer 2 in a fashion  that serves
> solicited node mcast addresses, placing the burden on another layer that,
> as it goes, does not have the adapted support in place...


You don't have to change ND to do that. All you need to do is either use
solicited-multicast node addresses over the multicast channel or, if the
subnet is SO large that ND requests are overwhelming (but that seems like a
LOT of ND traffic - how many clients do you need before this starts
happening?), use MLDv2 snooping and send the NS packets L2 unicast to their
destination.


> There is also the need for much faster DAD (not based on timing out)


What's the use case for faster DAD if you have optimistic DAD?